The present invention relates to an apparatus for inserting a weft on an air jet loom.
On an air jet loom, each weft is inserted into open sheds of warps while being entrained on air jet flow ejected by a main nozzle, which runs through an elongated column-shaped spaced defined by yarn guides or particular reeds arranged in the weft direction.
The air ejected by the main jet nozzle diverges into various directions and, consequently, a great deal of weft transportation energy of the air flow is lost on its course to the arrival side of wefts, thereby causing unstable travel of the weft.
Various systems have been proposed in order to mitigate such divergence of the air flow carrying weft.
In one proposal, particular type of reeds are used based on the recognition that a lowering in the flow velocity of the air is caused by leakage of the air out of the open shed of warps. In another proposal, auxiliary jet nozzles are used for supplying additional jet air into the open shed of the warp with the mouths of the nozzles opening in the travelling direction of weft. In yet another proposal, covers are arranged on both vertical sides of the open shed of warps.
Although these conventional systems well stabilize the travelling mode of weft, no increase in the travelling speed of weft can be expected. Conventionally, increase in the travelling speed of weft has been achieved by increasing air pressure at the main jet nozzle, i.e. the velocity of the air flow entraining the weft.
Velocity of the air flow increases to a certain extent in proportion to the corresponding increase in air pressure at the main jet nozzle. However, after reaching a velocity approximately equal to 290 to 300 m/sec, a further increase in air pressure does not accompany a corresponding increase in velocity of the air flow. To the contrary, some reduction in velocity of the air flow tends to occur, and the efficiency of weft transportation energy per power consumption lowers.
This lowering in efficiency is assumed to be caused by the following mechanism.
A main jet nozzle is generally comprised of a main tube and a needle rearwardly coupled to the main tube. The main tube has an axial terminal conduit opening in its front end which faces the warp shed and the needle has an axial yarn guide conduit forwardly communicating with the terminal conduit of the main tube. A forwardly converging throat is left between the main tube and the needle. This throat communicates upstream with a given supply source of compressed air and merges downstream in the terminal conduit of the main tube at the junction of the yarn guide conduit of the needle with the terminal conduit.
The compressed air of a pressure from 1.5 to 4.0 kg/cm.sup.2 surges into the terminal conduit via the throat and forms a jet air flow of a velocity from 290 to 300 m/sec. The travelling speed of the weft delivered from the yarn guide conduit of the needle is dependent upon this velocity of the air flow and the length of the terminal conduit formed in the main tube.
Increase in air pressure and the length of the terminal conduit, however, tends to cause the air flow within the terminal conduit to choke, which cuts down the velocity of the air flow and may induce reverse flow of air into the yarn guide conduit of the needle. The combination of these adversely affect stable travel of weft at high travelling speed.
For this reason, there is a critical value for travelling speed of the weft once the mechanical particulars of the apparatus are fixed and it is quite impossible to increase the travelling speed of weft beyond the critical value by increasing air pressure. In order to achieve a further increase in travelling speed of weft, it is necessary to use another main jet nozzle of different mechanical particulars, e.g. a main jet nozzle with a layer diameter of the terminal conduit and higher air pressure. This inevitably leads to the use of an unnecessary large amount of pneumatic energy.